#define _CRT_SECURE_NO_WARNINGS 1
#include<iostream>
using namespace std;
int main()
{
	int n;
	cin >> n;
	int a = 1, b = 1, c = 0;
	for (int i = 3; i <= n; i++)
	{
		c = a + b;
		a = b;
		b = c;
	}
	if (n == 1 || n == 2)
		cout << 1 << ".00" << endl;
	else
		cout << c << ".00" << endl;
	return 0;
}